Intravenous (hereafter “IV”) infusion apparatuses are used to deliver a variety of IV solutions to a patient. The IV solution to be delivered to the patient is typically contained in a bottle or flexible container that is fluidly connected to a fluid administration set. The fluid administration set includes a length of tubing designed to run from the bottle or flexible container to a cannula configured for insertion into the patient's blood vessel. Various fluid control devices such as clamps, valves, and/or drip chambers can be included along the length of the administration set. The drip chamber includes a drop former at its upstream end, a substantially transparent chamber through which drops are to fall, and an outlet port at its downstream end. The drop former portion is typically constructed to form drops having a predetermined volume. Many drip chamber manufacturers include details on their products specifying the drop size created in their drip chambers, and in some cases providing a correlation between the number of drops and the volume of fluid passing through the drip chamber.
For example, a drop former may be constructed such that 20 drops equals one milliliter. As the fluid is supplied to the drip chamber from the fluid reservoir, the drop former generates drops of the fluid that fall through the transparent chamber to the outlet port. The flow rate can be determined by counting the number of drops per unit time and then performing a calculation to determine the actual flow rate. For example, if forty drops are counted in a time period of one minute, and the specification of the drip chamber indicates that twenty drops equals one milliliter, then the calculation is that a flow rate of two milliliters per minute exists. Should the actual volume of each drop vary from that specified for the particular drip chamber device, the actual fluid flow rate to the patient will be affected.
The very existence of drops indicates that fluid is flowing in the fluid administration system. The falling drops can be visibly observed in the transparent chamber and counted over a unit of time to calculate the flow rate. The flow rate can be adjusted by a clamp or other device upstream of the drip chamber device, or by downstream means such as an infusion pump or a clamp. If an infusion pump is used, it will engage the administration set downstream of the drip chamber device and can be used to set a flow rate.
Typically, a medication in solution is prescribed at a particular drop rate or volumetric flow rate for a given patient. Maintaining a consistent drop rate or flow rate is desired so that the prescribed treatment is delivered correctly. However, many factors tend to cause the rate to change after it has been initially set. For example, the rate of drop formation is dependent on the head height/pressure of the fluid reservoir. Depletion of the fluid supply will tend to decrease the head pressure on the drop former and will cause a diminution in the rate of drop formation and flow. Vibration or shock may cause the rate controlling clamp to change its adjustment. An obstruction may find its way into the drop former causing the formation of smaller drops thus changing the rate of fluid flow.
Approaches for automating the monitoring process have been provided in the past. Many attempts have been made at providing an automated drop counter. While such systems have proved useful, they do not indicate by direct measurement the actual volume of the fluid detected. They only indicate that a drop has been detected. Such automated systems then use the drop volume specified by the manufacturer of the drip chamber to determine volume, which may not always be accurate.
Another approach for automating the monitoring process includes the inclusion of a mechanism for measuring the volume of drops passing through the drip chamber. For example, an array of photodetectors can be used to determine the size of the shadow of a drop as it passes in front of the detector. However, a variety of factors can interfere with accuracy of these systems, including the presence of condensation or splashed droplets on the interior wall of the drip chamber. Tilting of the drip chamber from its vertical axis may also affect the accuracy of the volumetric calculation by changing the distance between the photodetectors and the drops flowing through the drip chamber.
Accordingly, the inventors have identified a need in the art for a fluid control system that accommodates the variability inherent in the medication delivery environment, such as a hospital or clinic.